Effects of the flavone luteolin,isolated from Colchicum richii,on guinea-pig isolated smooth muscle and heart and on blood pressure and blood flow

The effects of the flavone luteolin, extracted from Colchicum richii, on guinea-pig isolated ileum, pulmonary artery, trachea, atrium, perfused heart, and on blood pressure and blood flow of anaesthetized guinea-pigs were studied. Luteolin (10^?5?3 × 10^?4 M) caused concentration-dependent relaxation of the tone of ileum, epinephrine-precontracted pulmonary artery and only mild relaxation of acetylcholine-precontracted trachea. These effects were not affected by pretreatment with 1 mM theophylline except in the ileum where theophylline shifted to the left the luteolin concentration-effect curve. Luteolin (3 × 10^?6?3 × 10^?4 M) caused an increase in the beating rate and the contractility of the spontaneously beating atrium and of the isolated perfused heart. Theophylline (1 mM) significantly inhibited the effects of luteolin on the atrium and the perfused heart. Luteolin, in doses of 0.3, 1.0, 1.5 and 5 mg/kg body weight had no effect on heart rate of anaesthetized guinea-pigs but caused depression of systolic and diastolic blood pressure except at the lowest dose used where there was a small increase in both parameters. Also, only the lowest dose (0.3 mg/kg) caused a small increase in blood flow. Larger doses of luteolin caused dose-related inhibition of blood flow. The effects of luteolin on blood pressure and blood flow were not affected by theophylline pretreatment (5 mg/kg). These observations suggest that the effects of luteolin may be tissue-specific and in the isolated heart they may be attributed to inhibition of cyclic AMP phosphodiesterase. The data further demonstrate that luteolin has potential cardiovascular effects that merit further investigation.